Circadian variation in the natriuresis produced by potassium intake in the rat

To determine if there was an endogenous circadian regulation of the renal natriuretic response to acute potassium loading, unanesthetized rats, either fed or fasted, were given an intragastric infusion of KCl over 100 min at the times of maximum and minimum circadian sodium excretion, i.e. in the early dark and early light phase of a 12 hour dark/light cycle. During KCl infusion plasma potassium concentration as well as sodium and potassium excretion progressively increased. Cumulative sodium excretion was greater in dark than light phase, and was greater in fed than fasted rats. Sodium excretion was greater at any given elevated level of plasma potassium in the dark than light phase. The results suggest that reported variations in the effects of high potassium diets on sodium excretion, blood pressure, or circulatory pathology in hypertension, may in part be explained by variations in the time of oral potassium intake.